It is the long-range purpose of this project to study the perinatal development of the functioning small intestine in normal and environmentally-, nutritionally- and hormonally-stressed animals. The topics of present interest which relate to the development of the normal functioning small intestine are: (1) ontogeny of lactate dehydrogenase isozymes, kinetic parameters and substrate/cofactor specificity during intestinal development, (2) characterization of the morphology and metabolism of isolated intestinal absorptive tip cells, (3) determination of the isozyme profile for beta-glucuronidase during intestinal development and after 1,2-dimethylhydrazine treatment, (4) differential susceptibility of isolated intestinal tip and crypt cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin induction, (5) mechanism of As-induced alterations of mitochondrial function in normal and alloxan-diabetic animals, and (6) monitoring the response of key intestinal enzymes to in vivo steroid treatments.